Michelle McKerral

Deficits in complex visual information processing after mild TBI: Electrophysiological markers and vocational outcome prognosis

Primary objective: To evaluate low-level to complex information processing using visual electrophysiology and to examine the latters prognostic value in regards to vocational outcome in persons having sustained a mild traumatic brain injury (mTBI). Research design/methods: Event-related potentials (ERPs) were recorded to pattern-reversal, simple motion, texture segregation and cognitive oddballparadigms from 17 participants with symptomatic mTBI at onset of specialized clinical intervention and from 15 normal controls. The relationship between abnormal electrophysiology and post-intervention return to work status was also examined. Main outcomes and results: Participants with mTBI showed a statistically significant (p< 0.05) amplitude reduction for cognitive ERPs and delayed latencies for texture (p< 0.05) and cognitive paradigms (p< 0.005) compared to controls. Furthermore, participants with mTBI presenting texture or cognitive ERP latency delays upon admission were at significantly (p< 0.01) greater risk of negative vocational outcome than mTBI participants with normal electrophysiology. Conclusions: The findings suggest that individuals with symptomatic mTBI can present selective deficits in complex visual information processing that could interfere with vocational outcome. ERP paradigms such as those employed in this study thus show potential for evaluating outcome prognosis and merit further study.

Texture segregation in traumatic brain injury––a VEP study

Visual evoked potentials (VEPs) were recorded to textures segregated by gradients in orientation or motion. Recordings were obtained in traumatic brain-injured (TBI) subjects and in normal controls. We analyzed both the low-level VEPs (llVEPs) evoked by homogenous stimuli, as well as the components associated with texture segregation (tsVEP) obtained through an appropriate linear combination. Our results suggest that the tsVEP, presumably higher up in the visual processing chain than the llVEP, is sensitive to TBI and can reveal further information as to the nature of possible information processing deficits after TBI. It could also help quantify cortical damage that is not revealed with more standard clinical tools.

Sexuality after traumatic brain injury: a critical review.

Brain injury can directly and indirectly affect important aspects related to sexuality and sexual function. In this critical review of the literature, traumatic brain injury (TBI) and sexuality are examined. A general review of the concept of sexuality and the neurological correlates of sexual function are proposed as a framework to understand the cognitive, behavioral and physical effects of TBI on sexuality and sexual function. Studies are then classified according to the participants enrolled and findings are presented from the professionals, the survivors, the patient/partners, and the non-injured spouses perspectives. Results are discussed taking into account methodological limitations and knowledge gaps. Next, implications for sexual rehabilitation for individuals with TBI are discussed. Finally, suggestions for future research and their pertinence for improving rehabilitation outcomes are considered.

Impact of divided attention during verbal learning in young adults following mild traumatic brain injury.

Primary objective: The goal of the present study was to assess the impact of mild traumatic brain injury (MTBI) on episodic memory performance in relation to attentional and executive control processes in young adults. Research design/methods: A verbal memory paradigm manipulating attentional load (full attention or divided attention) and semantic congruency between pairs of category-target words during encoding was administrated to 13 individuals with MTBI and 12 normal control participants. Environmental supports during retrieval (free recall, cued recall and recognition modes) were also manipulated. Main outcomes and results: Results show that recall performances of individuals with MTBI were similar to those of controls when words were encoded under full attention. In contrast, individuals with MTBI performed worse than control participants when encoding under divided attention, whatever the semantic link between pairs of words. Conclusions: By using a sensitive test, one was able to objectively measure subtle impairments in memory performance, suggesting a diminished availability of attentional resources after MTBI. Young adults’ learning of verbal material under divided attention might be compromised by the reduction of cognitive resources following MTBI. These findings are also discussed in light of different factors that can influence cognitive performance.

Delayed Early Primary Visual Pathway Development in Premature Infants: High Density Electrophysiological Evidence

In the past decades, multiple studies have been interested in developmental patterns of the visual system in healthy infants. During the first year of life, differential maturational changes have been observed between the Magnocellular (P) and the Parvocellular (P) visual pathways. However, few studies investigated P and M system development in infants born prematurely. The aim of the present study was to characterize P and M system maturational differences between healthy preterm and fullterm infants through a critical period of visual maturation: the first year of life. Using a cross-sectional design, high-density electroencephalogram (EEG) was recorded in 31 healthy preterms and 41 fullterm infants of 3, 6, or 12 months (corrected age for premature babies). Three visual stimulations varying in contrast and spatial frequency were presented to stimulate preferentially the M pathway, the P pathway, or both systems simultaneously during EEG recordings. Results from early visual evoked potentials in response to the stimulation that activates simultaneously both systems revealed longer N1 latencies and smaller P1 amplitudes in preterm infants compared to fullterms. Moreover, preterms showed longer N1 and P1 latencies in response to stimuli assessing the M pathway at 3 months. No differences between preterms and fullterms were found when using the preferential P system stimulation. In order to identify the cerebral generator of each visual response, distributed source analyses were computed in 12-month-old infants using LORETA. Source analysis demonstrated an activation of the parietal dorsal region in fullterm infants, in response to the preferential M pathway, which was not seen in the preterms. Overall, these findings suggest that the Magnocellular pathway development is affected in premature infants. Although our VEP results suggest that premature children overcome, at least partially, the visual developmental delay with time, source analyses reveal abnormal brain activation of the Magnocellular pathway at 12 months of age.

Neurophysiological correlates of auditory and language development: a mismatch negativity study.

During child development, physiological changes occur in the auditory cortex, which are reflected by differences in the electrophysiological signals. This study aimed to examine the age-related changes of the Mismatch Negativity component (MMN) in response to speech and non-speech stimuli in a cross-sectional design. Results revealed distinct patterns of activation according to stimulus type and age. Age-related differences for tone discrimination occurred earlier in childrens development than did the discriminative process for speech sounds. Therefore, networks involved in speech processing are still immature in late childhood and may be more vulnerable to physiological changes.

Visual Evoked Potentials and Reaction Time Measurements to Motion-reversal Luminance- and Texture-defined Stimuli

Purpose: Previous studies have suggested that compared to first-order (FO) motion stimuli, second-order (SO) motion stimuli required more cortical time to be processed. The purpose of this study was: 1- to verify this claim with Visual Evoked Potential (VEP) and eye-hand Reaction Time (RT) measurements and 2- examine if the VEP and RT responses are similarly modulated by the same trigger features of the stimuli. Methods: The VEPs and eye-hand RT for motion-reversal luminance- (first-order) and texturedefined (second-order) stimuli were recorded from ten normal human subjects. VEPs and RTs were measured for each motion class at eight different modulation depths (from 3 to 100%). Results: Our results reveal that for stimuli of low contrast levels, the SO–FO timing differences are approximately 100 ms (RT) or 20 ms (VEP), while for contrasts ≥ 15–20% (VEP) or ≥ 50% (RT), the SO–FO difference is no longer significant (p < 0.007), suggesting either that the brain can no longer distinguish SO from FO stimuli or that in spite of the added complexity of SO stimuli the brain takes equal time to process both. Conclusion: Interestingly, the above contrast discrepancy in SO–FO resolution threshold suggests that, compared to the VEP, the more psychophysical RT measurement can process and thus distinguish a larger spectrum of motion stimuli, thus further confirming the latter measure of the retinocortical processing time as a valid alternative to the VEP.

Monocular contribution to the peak time of the binocular pattern visual evoked potential.

The contribution of each monocular pathway to the timing of the binocular pattern visual evoked potential was assessed in situations where a significant interocular timing discrepancy was observed. Monocular and binocular pattern visual evoked potentials to 0.5° checks were recorded from normal subjects, normal subjects in whom one eye was blurred, patients with monocular amblyopia, and patients with resolved unilateral optic neuritis. Normal subjects showed facilitation, while suppression was evidenced in subjects with monocular blurring. In patients with amblyopia, the affected pathway had no effect on binocular pattern visual evoked potential latency, suggesting that the amblyopic eye was suppressed. In contrast, all patients with optic neuritis showed binocular averaging. Our results show that different forms of binocular interaction are evidenced in normal subjects, in amblyopia and in optic neuritis, and suggest that a comparative analysis of monocular and binocular pattern visual evoked potential peak times brings valuable information to the clinical evaluation that could be used to distinguish disease processes further.

Luminance- and texture-defined information processing in school-aged children with autism.

According to the complexity-specific hypothesis, the efficacy with which individuals with autism spectrum disorder (ASD) process visual information varies according to the extensiveness of the neural network required to process stimuli. Specifically, adults with ASD are less sensitive to texture-defined (or second-order) information, which necessitates the implication of several cortical visual areas. Conversely, the sensitivity to simple, luminance-defined (or first-order) information, which mainly relies on primary visual cortex (V1) activity, has been found to be either superior (static material) or intact (dynamic material) in ASD. It is currently unknown if these autistic perceptual alterations are present in childhood. In the present study, behavioural (threshold) and electrophysiological measures were obtained for static luminance- and texture-defined gratings presented to school-aged children with ASD and compared to those of typically developing children. Our behavioural and electrophysiological (P140) results indicate that luminance processing is likely unremarkable in autistic children. With respect to texture processing, there was no significant threshold difference between groups. However, unlike typical children, autistic children did not show reliable enhancements of brain activity (N230 and P340) in response to texture-defined gratings relative to luminance-defined gratings. This suggests reduced efficiency of neuro-integrative mechanisms operating at a perceptual level in autism. These results are in line with the idea that visual atypicalities mediated by intermediate-scale neural networks emerge before or during the school-age period in autism.

COMMENTS ON THE TASK FORCE REPORT ON MILD TRAUMATIC BRAIN INJURY: JOURNAL OF REHABILITATION MEDICINE SUPPLEMENT 43

The results of the Best Evidence Synthesis conducted by the World Health Organization Collaborating Centre Task Force on Mild Traumatic Brain Injury (MTBI), published in this journal in 2004 (suppl. 43), reflect work of exceptional magnitude. The analysis of existing scientific research literature on all aspects of MTBI (diagnosis, prognosis and treatment) was greatly needed. However, the results of such a process merit strong caution as to their possible clinical applications. Thus, the following points should be considered: